For the deployment of electronic commerce and on-line banking services, information security techniques are of paramount importance. As will be seen from the prior art cited hereafter, they are also important for the protection of computer networks and the authentication of subscribers of mobile telephone service. A general scheme emerges for the organization of such electronic authentication applications, despite the diversified vocabulary used in different application areas. There is first a central database under the operational control of a service organization whose trustworthiness is commensurate with the issues at stake. Then, there are the potential clients, individuals or organizations. The general function of a registration process is to make a given client known by the service organization in such a way that the subsequent routine processing of transactions is automated and efficient. The clients have access to electronic apparatus through which they conduct their ordinary activities. A registration process provides the client with secret authentication information. This secret can be a Personal Identification Number (PIN), a private key for a digital signature algorithm, or a secret cryptographic key shared between the client and the service organization. While a PIN can be remembered by a normal person, the two other forms of authentication secret require a digital memory of some sort. The present invention is mainly concerned with the registration process when a shared secret authentication key is used.
Ultimately, transaction authentication is effective if it secures the legal tie or bind between a bank account withdrawal and the account holder's liability, while barring access to the funds by defrauders. Since the account holder is a legal person rather than a digital apparatus, the required chain of evidence is a two-tiered authentication bind: 1) the logical bind between the account holder (or the account holder agent) and a cryptographic operation performed by a digital apparatus, and 2) the bind between this said cryptographic operation and the transaction historic records of the financial institution. Within its scope of a registration process, the present invention addresses these two aspects of transaction authentication.
The distinction between "secret key cryptography" and "public key cryptography" is well known in the prior art. In the present disclosure, we reserve the term "secret" to data shared in confidence between parties in a secret key cryptography arrangement, and respectively the terms "private" and "public" to the private and public components of a private/public key pair of the type used for digital signatures or public key encryption from the field of public key cryptography.
The elementary cryptographic operation used in transaction authentication can be DES encryption of a secret Personal Identification Number (PIN) entered at a Point of Sale terminal (POS terminal), with cryptographic integrity protection applied to the whole transaction (typically with a Message Authentication Code based on DES and a secret key). In that case, a long-term secret key has to be established initially between the POS terminal and the data processing center responsible for transactions initiated from this POS terminal (normally under the control of the merchant's financial institution). This long-term secret key is of the type that can be established with the present invention. U.S. Pat. No. 4,771,461 discloses a procedure for this secret key establishment.
This prior art of U.S. Pat. No. 4,771,461 suffers from a number of intrinsic limitations. First and foremost, there is the following explicit security weakness (column 16 lines 1 to 6): "The general exposure of the procedure is that an opponent can always initiate a successful sign-on from his location with his terminal, provided that the real terminal never signs on before T2 and does not report this to the KDC [Key Distribution Center]. In that case, the fake terminal can continue to operate indefinitely."
More generally, the procedure of U.S. Pat. No. 4,771,461 appears outdated when one considers the level of sophistication reached by adversaries of actual cryptosystems. See for instance the article by Ross J. Anderson, Liability and Computer Security: Nine Principles (in Computer Security--Esorics '94, Third European Symposium on Research in Computer Security, November 1994, LNCS 875, Springer Verlag, PP 231-245), the article by Martin Abadi, and Roger Needham, Prudent Engineering Practice for Cryptographic Protocols (in 1994 IEEE Symposium on Research in Security and Privacy, IEEE, 1994, PP 122-136), and the article by Ross J. Anderson, and Roger Needham, Robustness Principles for Public Key Protocols (in Advances in Cryptology, CRYPTO'95, LNCS 963, Springer Verlag, 1995, PP 236-247). Nonetheless, U.S. Pat. No. 4,771,461 has the merit of stressing the importance of data integrity protection for the initial establishment of cryptographic keys.
There are also operational limitations in the procedure of U.S. Pat. No. 4,771,461. Despite the acknowledgment that courier services for secret key distribution are expensive and burdensome, it is not clear how courier services can be avoided altogether. They may be required because the POS terminals can be loaded with a terminal identifier and/or a public key at a central location. Courier services or another form of alternate secure channel may also be required for some instructions to a person because these instructions may contain sensitive information specific to each POS terminal. Moreover, the explicit operational delays introduced by this prior art have a negative impact on the value of the procedures.
The U.S. Pat. No. 5,784,463 uses public key cryptography to establish some long term cryptographic keys in a manner analogue to U.S. Pat. No. 4,771,461, but it lacks facilities for verification of identity such as the time windows in U.S. Pat. No. 4,771,461. In other words, the U.S. Pat. No. 5,784,463 embeds no procedural countermeasure against the threat of theft of identity. Without any such countermeasure, a would-be defrauder simply needs the electronic version of identification information needed for registration in order to attempt an impersonation attack.
The U.S. Pat. No. 5,216,715 on lines 14 to 18 on column 5 (and on lines 16 to 23 on column 6) refers to a known procedural protection used for remote user authentication at the outset of a telephone call, just after some session key establishment protocol, that is the verbal confirmation that some check value agree on both ends of the telephone call. The assurance provided by this procedural authentication step is valid for the duration of the telephone call only. For a security system to be as unintrusive as possible, routine operations such as a telephone call setup should use fully automated security mechanisms; procedural steps should be used sparingly, e.g. to the initial registration of legitimate users of the system. Indeed, the procedural step for remote telephone operator identification as in U.S. Pat. No. 5,216,715 is typical of very high security telephone sets. In addition, the procedural verification of identity in U.S. Pat. No. 5,216,715 does not work if the call is established with a voice mailbox.
In the field of wireless subscriber registration, the U.S. Pat. No. 5,077,790 discloses a procedure based on the establishment of a "key code" that is a secret key shared between a portable telephone and the network controller. Upon verification of the applicant's credit, an help desk agent provides a "link identification number" that binds the credit approval to the subsequent download of the definitive "subscriber identification number", this download being cryptographically protected with the initial "keycode". This procedure is inconvenient due to the manual operations involved in the establishment of the "key code" and might be vulnerable to eavesdropping because every security critical information is transmitted over the air and while no public key cryptography is involved.
In many cases, security systems features create more inconvenience to the users than effective protection. This is the case in the U.S. Pat. No. 5,386,468 that discloses an electronic identification registration procedure where the typing of user application information on a communication terminal keyboard is duplicated by filling a user application form and mailing it. This duplicate work is inconvenient because the paper processing actually delays the reply in the query/reply protocol used for registration. One can assume that U.S. Pat. No. 5,386,468 is practiced without the procedural step (paper processing) for which no clear purpose is disclosed. In any event, the key management burden in the manufacturing and distribution of terminals is significantly higher in U.S. Pat. No. 5,386,468 than in U.S. Pat. No. 4,771,461.
The elementary cryptographic operation used in transaction authentication can also be a digital signature from the field of public key cryptography, in which case a representative description of the prior art may be found in the Working Draft ANSI standard X9.30-199x Public Key Cryptography Using Irreversible Algorithms for the Financial Services Industry: Part 3: Certificate Management for DSA (by the Accredited Standards Committee X9-Financial Services, ANSI ASC X9, American Bankers Association, Washington, D.C., Nov. 19, 1994 document N24-94). The present invention alleviates the traditional burden of secret key distribution, and thus suggests the avoidance of the public key infrastructure described in the mentioned Working Draft ANSI standard X9.30-199x. Indeed, the financial industry has been operating on a centralized trust model for decades, and the adoption of public key paradigms may be expected to remain low.
Turning now to the logical bind between the account holder (or the account holder agent) and a cryptographic operation performed by a digital apparatus, one way to let the account holder control the use of a cryptographic key is to store it on a hand held memory device in credit card format, or in a format suitable for attachment on a key ring, or any other small size format. Thus, the account holder is relieved from the obligation to control the access to a fixed apparatus like a computer system, or a luggage-size apparatus like a portable personal computer. When the hand-held memory device contains intrinsic data access control features, it falls into the smart card category. This usually requires a rudimentary microprocessor along with the memory device. With further sophistication, a hand held electronic device may embed sufficient processing power and/or memory to be perform complete cryptographic operations. In the latter case, the security is enhanced by avoiding the threat of malignant software modifications. The present invention facilitates the establishment of the secret key to be loaded on hand held devices where the prior art required the use of centralized key loading facilities, and/or secure transmission of secret keys using trusted courier services. The present invention may allow the avoidance of centralized smart card personalization operation.
The centralized trust model typical of the financial industry is assumed by the United States regulatory environment for consumer protection in the case of electronic fund transfers. The field of the present invention is more specifically covered by EFTA, Electronic Fund Transfer Act, Title IX of the Customer Credit Protection Act, (15 U.S.C. .sctn.1601 et seq.) and Regulation E. Electronic Fund Transfers, (12 C.F.R. .sctn.205) Section 205.5 which deals with the issuance of access devices used for customer-initiated EFT. In some circumstances and according to these rules, a secret key (established with the help of cryptographic protocols) may fall under the legal definition of an access device. In such a case, a verification of the customer identity is prescribed as a condition for the final validation of the secret key for EFT transactions. An object of the present invention is to facilitate the issuance (of access devices) complying with the EFTA Regulation E or similar rules.
A difficulty with key management methods that require centralized configuration or personalization is the implied restrictions on the channels of distribution. For consumer electronics, computer products, and software devoid of security functions, a myriad of channels are possible: catalog sales, retail stores, large discounters, and the like, the list being endless. If an item (like an access device for an EFT service) has to be prepared for a specific customer by trusted personnel according to procedures dictated by a financial institution, the possible channels of distribution are very few, if any, besides courier shipment by the financial institution. U.S. Pat. No. 5,557,679 is an attempt to use retail outlets for the distribution of subscriber identity modules (portable memories used for mobile telephone subscriber authentication). The present invention broadens the choices of acceptable channels of distribution for authentication devices.
In U.S. Pat. No. 5,557,679, secret keys are pre-established to secure a network of retail locations where the key loading operation is performed. There is no capability for the fully distributed scenario where the target electronic devices are remotely located from any (already) secured system. Secret key schemes that avoid the use of courier services in a fully distributed scenario are conceivable if the target electronic devices are already loaded with a common, fixed key "hidden by being included in the [device] programmable read only memory (PROM) at manufacturing level", as in U.S. Pat. No. 5,539,824. Such a scheme is generally considered not so secure, except perhaps when offered by a very reputable supplier.
The famous Diffie-Hellman cryptosystem described in U.S. Pat. 4,200,770, and the recent similar proposals found in U.S. Pat. Nos. 5,583,939 and 5,375,169 do not provide remote party authentication and secret key freshness simultaneously. Indeed the "public key" of a Diffie-Hellman exchange is usually considered a short-lived cryptographic value, and the authentication potential of the Diffie-Hellman exchange is not used. For instance, U.S. Pat. No. 5,020,105 applies Diffie-Hellman to the task of establishing a secret authentication key, but does not provide facilities for verification of account holder identity. Moreover, the processing load implied by the original Diffie-Hellman cryptosystem is large, while the security of U.S. Pat. Nos. 5,583,939 and 5,375,169 is questionable or uncertain. The recent article by Lein Ham, Digital signature for Diffie-Hellman keys without using a one-way function (in Electronics Letters, Jan. 16, 1997, Vol. 33, No. 2, pp. 25-126) discloses a noteworthy attempt at enhancing the Diffie-Hellman scheme with authentication properties.
It is logical that the disclosure in U.S. Pat. No. 4,771,461 stresses the need for data integrity in the key loading operation, and at the same time uses a public key cryptosystem, RSA, with a long-term public key assigned to the financial institution. This public key participates in the authentication of the financial institution to the benefit of the client-side of the secret key establishment. The security of this prior art depends on the unpredictability of the random number source on the client-side. The use of random sources for cryptographic key material has been recognized as a potential source of security flaws.
Any scheme where the client-side of the session key establishment already has a long term public key is likely to address a need different from the present invention, based on the premises of public key cryptography. U.S. Pat. No. 5,406,628 may be a good example.
Last, but not least, is the disclosure by the present Applicant, of the Probabilistic Encryption Key Exchange (PEKE) cryptosystem in Canadian patent application 2,156,780 (entitled Apparatus and Method for Cryptographic System Users to Obtain a Jointly Determined, Secret, Shared, and Unique Bit String, filed on Aug. 23, 1995, laid-open to the public on Sep. 23, 1995), in an article by Thierry Moreau, Probabilistic Encryption Key Exchange (in Electronics Letters, Vol. 31, number 25, Dec. 17, 1995, pp 2166-2168), and in a technical report by Thierry Moreau, Automated Data Protection for Telecommunications, Electronic Transactions and Messaging using PEKE Secret Key Exchange and Other Cryptographic Algorithms, Technology Licensing Opportunity (revision 1.1, CONNOTECH Experts-Conseils Inc., Montreal, Canada, March 1996, with legal deposits in the National Library of Canada, where it was not available to the public before April 1997, and in the National Library of Quebec, where it was made available to the public some time between November 1996 and January 1997). The PEKE cryptosystem is based on the Blum-Goldwasser probabilistic encryption scheme explained in an article by Manuel Blum and Shafi Goldwasser, An Efficient Probabilistic Public-key Encryption Scheme which Hides All Partial Information (in Advances in Cryptology: Proceedings of Crypto'84, Springer-Verlag, 1985, pp 289-299). The PEKE cryptosystem has been disclosed so far for session key establishment with no facilities for the verification of identity. Indeed, transaction authentication using PEKE is suggested in the mentioned technical report by Thierry Moreau, but using a preset shared secret password as the basis for authentication, and PEKE for session key establishment. For the present invention, the PEKE cryptosystem is one of three alternate cryptosystems, the other two being conventional public key encryption (e.g. RSA, in U.S. Pat. No. 4,405,829), and the Lein Harn's improvement to the Diffie-Hellman key exchange in the mentioned article by Lein Harn.
The commonly used public key cryptosystems use arithmetic operations on large integers and especially the modulus (the remainder of an integer division). To make these computations relatively efficient, the use of the Montgomery modulo reduction algorithm is relatively known in the prior art, see the original article by Peter L. Montgomery, Modular Multiplication Without Trial Division (in Mathemetics of computations, Vol. 44, no. 170, April 1985, pp 519-522). Two implementations are disclosed in the article by Stephen R. Dusse and Burton S. Kaliski Jr., A Cryptographic Library for the Motorola DSP56000 (in Advances in Cryptology, Eurocrypt'90, Lecture Notes In Computer Science no. 473, pp 230-244, Springer-Verlag, 1990) and in the article by S. E. Eldridge and Colin D. Walter, Hardware Implementation of Montgomery's Modular Multiplication Algorithm (in IEEE Transactions on Computers, Vol. 46, no. 6, June 1993, pp 693-699). These two detailed accounts of the Montgomery algorithm implementation are targeted, respectively, at digital signal processors with peculiar instruction sets, and at dedicated integrated circuit design. Adaptations of this prior art are useful when the Montgomery algorithm is implemented on a general purpose digital processor.